The present invention relates to a bus coupler which operates with a transformer and with a comparator that is connected downstream in a signal-processing branch.
Such a bus coupler is disclosed (FR-A-2,443,770, FIG. 1). The bus coupler of the comparator operates there with a statically set threshold. This data bus system operates with a terminating impedance at the end of each bus line.
In the case of data bus systems, it is known to pass both data and information signals together with a supply voltage on a bus conductor. Such a system is disclosed in EP-A-0,365,696. In this case, the bus conductor is supplied from a voltage supply having a DC voltage which is balanced with respect to ground. A plurality of subscribers can be connected to the bus conductor. Those subscribers can pick off both the supply voltage and an information signal. Information signals can also be transmitted to the bus by the subscribers. A transformer with a capacitor is used for separating received information signals or for emitting information signals to the bus. In the case of such an inductive bus coupler, the capacitor separates the potentials of the energy supply for the on-board network and closes the signal path through the transformer winding on the bus side. The system operates without any terminating impedance at the end of the bus line.
For transmission of bit pulses, the inductance L of the coupler should be as large as possible, since the load of a transmitter which operates on the bus comprises a very large number of parallel-connected stations, each with their own bus coupler. At the same time, the total load impedance should be as low as possible, so that the magnetization current surge is not too large. If a comparator is used in the signal-processing branch of a bus coupler, relatively powerful signals, such as those from transmitters operating close to the bus, should, on the other hand, be received and even powerful interference signals should be attenuated or suppressed.